This invention relates generally to trickle irrigation units for providing a relatively slow, substantially drip flow rate of water for irrigating crops and the like. More specifically, this invention relates to an improved trickle irrigation unit, particularly of the type described in U.S. Pat. No. 3,954,223.
A variety of so-called trickle irrigation units are known for use in supplying water at a relatively slow, substantially drip flow rate to irrigate crops or the like without significant evaporation and/or erosion of soil. Such trickle irrigation units are typically installed along the length of an elongated water supply conduit at predetermined points at which irrigation water is desired, such as directly at the bases of individual plants, whereupon water under relatively high pressure is supplied to the conduit for flow into and through the irrigation units. The irrigation units are designed each to permit passage of a relatively small portion of the water within the supply conduit while substantially reducing the pressure thereof such that the water is emitted from the unit without spraying at a flow rate such as on the order of about one-half gallon per hour.
In some trickle irrigation units, such as that shown and described in U.S. Pat. No. 3,954,223, the unit includes an internal pressure chamber for receiving water under pressure from a water supply conduit and a resilient valve flap for controlling the flow of water from the pressure chamber to an outlet port. More particularly, the valve flap overlies a circular outlet port and a shallow channel including a smaller central outlet groove at one side of the pressure chamber, wherein the valve flap cooperates with the channel and groove to define a flow path communicating between the pressure chamber and the outlet port. When water pressure within the pressure chamber is relatively low, such as when a water supply is initially turned on, the valve flap remains substantially undeformed to permit a relatively high flushing flow through the shallow channel and the outlet groove to the outlet port to wash grit and the like from the unit. However, when the water pressure is relatively high, the valve flap deforms into the channel to reduce the cross-sectional area of the flow path to the comparatively smaller area of the outlet groove. This reduced flow path area functions as an orifice to limit water flow to the outlet port to a relatively low-pressure, substantially drip rate which can be maintained substantially constant throughout a range of relatively high water pressures by designing the valve flap for sufficient flexibility for pressure compensating movement partially into the outlet groove to alter the flow area thereof generally in inverse relation to water pressure.
In trickle irrigation units of this general type, the resilient valve flap thus deforms into the outlet port, the shallow channel, and the outlet groove with a magnitude of deformation directly proportional to the pressure within the pressure chamber. Since the outlet port is significantly larger in cross-sectional area than the outlet groove to permit grit passage during low pressure flushing, flap deformation into the outlet port at higher water pressures is therefore substantially greater than the deformation of the flap into the outlet groove. As a result, at relatively high water pressures, deformation of the valve flap into the outlet port can be sufficient to block or severely restrict the downstream end of the outlet groove which opens into the outlet port thereby interferring with the desired operation of the irrigation unit.
The present invention overcomes these problems and disadvantages by providing an improved trickle irrigation unit generally of the type described, wherein the outlet port is specially contoured to permit grit passage during low pressure flushing while preventing excessive deformation of the valve flap into the outlet port at higher water pressures thereby preventing undesirable blockage of the downstream end of the outlet groove.